1. FILTRATION 1

2. DEFINITION Filtration is a mechanical or physical operation which is used for the separation of solids from fluids (liquids or gases) by interposing a medium through which only the fluid can pass. After filtration the filtrate is transparent liquid free from insoluble solids, colloidal hazes, or insoluble liquid drops 2

3. CLARIFICATION The term clarification is used when the solids present in the liquid is very small and they do not exceed 1% and filtrate is the required product 3

4. FEED OR SLURRY The suspension of solids and liquids to be filtered is known as feed or slurry FILTER MEDIUM The porous medium through which the slurry is forced to pass is called filter medium 4

5.  RESIDUE The solids collected on the filter medium is referred to as residue  FILTERATE Clear liquid which passes through the filter is called filtrate 5

6. TYPES OF FILTRATION Three 1)Surface filtration 2)Depth filtration 3)Cake filtration 6

7. 1)Surface filtration:  Common process  It is a screening action by which pores or holes of the medium prevent the passage of solids.  Substances to be removed has larger size than the pore size of porous medium.  So particles can’t pass via pores & retain on filter media and clear liquid is obtained.  Mechanisms responsible are “STRAINING” and “IMPINGEMENT” 7

8. 2) Depth Filtration  Slurry penetrates to a point where the diameter of solid particles is greater than that of the tortuous void or channel.  The solids are retained with a gradient density structure by physical restriction or by adsorption properties of the medium  Mechanism is “ENTANGLEMENT” 8

9. Surface and Depth Filtration : 9

10. 3) Cake Filtration  A filter consists of a coarse woven cloth through which a concentrated suspension of rigid particles is passed so that they bridge the holes and form a bed.  Diatomite (100µm). This cake can remove sub micrometer colloidal particles with high efficiency. 10

11. DARCYS LAW : It may be expressed as: dV / dt = KA∆P /ul V = volume of filtrate, t = time of filtration, K = constant for the filter medium and filter cake, A = area of filter medium, P = pressure drop across the filter medium and filter cake, u = viscosity of the filtrate, and l = thickness of cake. 11

12. FACTORS INFLUENCING FILTRATION  Surface Area of the Filter Medium  Pressure Drop Across the Filter Medium  Viscosity of Filtrate  Resistance of Filter and Cake 12

13. Filter Media The surface upon which solids are deposited in a filter is called the “Filter medium” Chemically inert High resistance power for the solids Should have sufficient mechanical strength to withstand filtration pressure Should absorb negligible amount of dissolve material Should have resistance for the corrosive action of the liquid 13

14. SELECTION OF APPROPRIATE FILTER MEDIA:  Must effectively retain the solid particles.  Should not be leakage of solid particles via filter media.  Should be chemically inert.  Should be physically stable.  Should be cost effective. 14

15. Classification of filter media 1- Woven filters: these include a- wire screening. b- fabrics of cotton, wool, nylon. Wire screening e.g. stainless steel is durable, resistance to plugging and easily cleaned. Cotton : Backing for paper/felts in plate & frame filters Nylon : Unaffected by mold, fungus, bacteria Teflon : Almost chemically inert. Can withstand elevated temperatures 15

16. 2 - Non- woven filters:  Felts : Fibrous mass that is free from bonding agents and mechanically interlocked to yield specific pore diameters that have controlled particle retention  Bonded fabrics : are made by binding textile fibers with resins, solvents and plasticizers. But was not widely accepted because of interactions with the additives  Kraft paper: Pharmaceutical grade. Has limited use only in plate & frame filters, Horizontal plate filters. 16

17. 3- Membrane filters:  These are basic tools for micro-filtration, useful in the preparation of sterile solutions. These filters are made by casting of various esters of cellulose, or from nylon, Teflon, polyvinyl chloride. The filter is a thin membrane with millions of pores per square centimeter of filter surface.  150 microns thick. 40 times faster filtering. 17

18. 4- Cartridges : are economical and convenient.  Available in pore size of 100µm to even less than 0.2µm.  Used only for filtration when low % of solids are present in the liquid that is to be filtered. 1. Surface Type : Made up of Ceramic, Porcelain, Sintered metal 2. Depth Type : These are disposable items. -Made up of Cotton, asbestos, cellulose 18

19. Filter Aids : Usually, the resistance to flow due to the filter medium itself is very low, but will increase as a layer of solids builds up, blocking the pores of the medium and forming a solid cake. The objective of the filter aid is to prevent the medium from becoming blocked and to form an open, porous cake, so reducing the resistance to flow of the filtrate. The particles must be inert, insoluble, incompressible, and irregular shaped. The following filter aids may be used:  Diatomite ( Kieselguhr ), obtained from natural siliceous deposits.  Perlite, it is an aluminium silicate.  Cellulose, Asbestos, Talc, Paper pulp, Bentonite, Fullers Earth 19

20. Filter aids may be added in two ways:  1-Pre- coating technique: By forming a pre-coat over the filter medium by filtering a suspension of the filter aid.  2-Body- mix technique: A small proportion of the filter aid (0.1-0.5 %) is added to the slurry to be filtered. This slurry is re circulated through the filter until a clear filtrate is obtained, filtration then proceeds to completion. 20

21. CLASSIFICATION OF FILTRATION EQUIPMENT : Based on the application of External Force : 1.Pressure Filters : Plate & Frame filter press, Meta filter 2.Vacuum Filters : Filter Leaf 3.Centrifugal Filters : Perforated Basket Centrifuge, Semi-continuous Centrifuge 21

22. Based on Operation of Filtration : 1)Continuous filtration : Discharge and filtrate are separated steadily and uninterrupted. 2)Discontinuous filtration : Discharge of filtered solids is intermittent. Filtrate is removed continuously. The operation should be stopped to collect the solids Based on the nature of filtration : 1)Cake filters : Remove large amount of solids 2)Clarifying filters : Remove small amount of solids 22

23. 3) Cross-flow filters : Feed of suspension flows under pressure at a fairly high velocity across the filter medium. 23

24. Equipment Laboratory Scale vacuum Filter paper Large Scale Plate and FrameHorizontal Plate 24

25. Pressure Filters Due to the formation of cakes of low permeability, many types of slurry require higher pressure difference for effective filtration than can be applied by vacuum techniques. Pressure filters are used for such operations. However, high operational pressures, may prohibit continuous operation because of the difficulty of discharging the cake while the filter is under pressure. Example is plate and frame filter press, Filter press 25

26. Plate and Frame Filter Press This press is made up of two units, known respectively as plates and frames, with a filter medium, usually filter cloth, between the two. The frame is open, with an inlet for the slurry, while the plate has grooved surface to support the filter cloth, and with an outlet for the filtrate. 40 ~ 150 lb/in 2 ΔPΔP Canvas 26

27. 27

28. Working :  The slurry enters the frame from the feed channel  The filtrate passes through the filter medium on to the surface of the plate while the solids form a filter cake in the frame.  The filtrate then drained down the surface of the plate, between the projections on the surface and escapes from the outlet.  Filtration is continued until the frame is filled with filter cake, when the process is stopped, the frame emptied, and the cycle re-started. 28

29. Advantages &disadvantages Advantages: Construction is very simple and a wide variety of materials can be used. It provides a large filtering area in a relatively small floor space. It is versatile, the capacity being variable according to the thickness of the frames and the number used. The construction permits the use of considerable pressure difference. Efficient washing of the cake is possible. Operation and maintenance is straightforward, because there no moving parts, filter cloths are easily renewable and, because all joints are external, any leaks are visible and do not contaminate the filtrate. 29

30. Disadvantages: It is a batch filter, so it is a time consuming. The filter press is an expensive filter, the emptying time, the labour involved, and the wear and tear on the cloths resulting in high costs. Operation is critical, as the frames should be full, otherwise washing is inefficient and the cake is difficult to remove. The filter press is used only for slurries containing less about 5 % solids 30

31. Cartridge Filter : Cartridge filter is a thin porous membrane in which pre filter and membrane filter are combined into a single unit. The filtration action is mainly sieve-like and the particles are retained on the surface Working : The slurry is pumped into cartridge holder. It passes through cartridge filter unit by the mechanism of straining. The clear liquid passes to the centre and moves up to collect through the outlet. Can filter 1,000 to 15,000 liters of sterile solution per hour 31

32. Centrifuge Filter:  Filtration centrifuge is a centrifuge in which solids retain on the porous medium based on the difference in the densities of the solid and liquid phases. Perforated basket centrifuge :  Extensively used for separating crystalline drugs (Aspirin) from the mother liquor.  Remove unwanted solids from a liquid. E.g., Precipitated proteins are removed from insulin.  Sugar crystals are separated. 32

33. Vacuum filters : Vacuum filters operate practically at higher pressure differentials than gravity filters. Rotary vacuum filter and the leaf filter are most extensively used. The leaf filter: The leaf filter is consisting of a frame enclosing a drainage screen or grooved plate, the whole unite being covered with filter cloth. The outlet for the filtrate connects to the inside of the frame, the general arrangement is shown in the Fig. which represents a vertical section through the leaf. The frame may be circular, square or rectangular shapes. Working: The leaf filter is immersed in the slurry and a receiver and a vacuum system connected to the filtrate outlet. Slurry passed through the filter cloth and finally filtrate enters the Drainage canal and goes through outlet into the receiver. Air is passed to flow in reverse direction which facilitates removal of cake 33

34. 4- The filter can be modified by employing a suitable number of unites. 5- The leaf filter is most satisfactory if the solids content of the slurry is no too high, 5 % being a suitable maximum. 6- Labour costs for operating the filter are comparatively moderate. An alternative method is to enclose the filter leaf in a special vessel into which the slurry is pumped under pressure. A number of leaves are connected to a common outlet, to provide a large area for filtration e.g. Sweet land filter. Advantages: 1- The slurry can be filtered from any vessel. 2-The cake can be washed simply by immersing the filter in a vessel of Water. 3- Removal of the cake is facilitated by the use of reverse air flow. 34

35. Rotary vacuum filter (Rotary filter) In large –scale operation, continuous operation is sometimes desirable and it may be necessary to filter slurries containing a high proportion of solids. The rotary filter is continuous in operation and has a system for removing the cake that is formed, so, it is suitable for use with concentrated slurries. It is a metal cylinder mounted horizontally, the curved surface being a perforated plate, supporting a filter cloth. Internally, it is divided into several sectors and a separate connection is made between each sector and a special rotary valve. Drum may be up to 3 meters in diameter, 3.5 meters in length and gives a surface area of 20 meter square. 35

36. Operation: The drum is immersed to the required depth in the slurry, which is agitated to prevent settling of the solids, and vacuum is applied to those sectors of the drum which is submerged. A cake of the desired thickness is produced by adjusting the speed of rotation of the drum. Each sector is immersed in turn in the slurry and the cake is then washed and partially dried by means of a current of air. Finally, pressure is applied under the cloth to aid the removal of the cake. Removal of the washed and partially dried cake is affected by means of a doctor knife. 36

37. Advantages & disadvantages of rotary drum filter Advantages: 1-The rotary filter is automatic and is continuous in operation, so that the labour costs are very low. 2- The filter has a large capacity, so it is suitable for the filtration of highly concentrated solutions. 3- Variation of the speed of rotation enables the cake thickness to be controlled. 4- Pre-coat of filter aid could used to accelerate the filtration rate. Disadvantages: 1- The rotary filter is a complex piece of equipment, with many moving parts and is very expensive,. 2- In addition to the filter itself, some accessories are connected, e.g, a vacuum pump, vacuum receivers, slurry pumps and agitators are required. 3- The cake tends to crack due to the air drawn through by the vacuum system, so that washing and drying are not efficient. 4- Being a vacuum filter, the pressure difference is limited to 1 bar and hot filtrates may boil. 5- It is suitable only for straight- forward slurries 37

38. Uses: 1- The rotary filter for continuous operation on large quantities of slurry. 2- Suitable for slurry contains considerable amounts of solids in the range 15-30%. Examples of pharmaceutical application include the collection of calcium carbonate, magnesium carbonate, and starch, and the separation of the mycelium from the fermentation liquor in the manufacture of antibiotics 38

39. Continuous Rotary Vacuum Filter : 39